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05-19-2018, 11:17 AM
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Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,189
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wow
I fly for a living and you guys are scaring me...
Just for a couple of data points:
There were MILLIONS of hours flown safely in the B-727, and it had human intervention required..."Protect Essential" was the name of the game.
The B-757 and 767 have automatic switching but things can STILL go dark requiring human intervention.
The B-717 has uninterrupted power transfer systems and things STILL go dark, usually requiring a reboot of the system.
Let's not even mention the Airbus electrical system!
and let's not forget the MILLIONS of safely flown IFR hours in GA aircraft with simplistic electrical systems.
In aviation, there is ALWAYS a risk, and as these pages demonstrate, no matter what idea someone comes up with there will always be someone there to shoot it down.
I would propose that these "experts" provide their own designs and let the crowd have a stab at shooting them down...
I am not an electrical expert but for discussion's sake, here is my example. My design is that of a J-3 Cub with no electrical system...oh, wait, what if there is a failure of the switch hooked to the P leads?...
Seems like, if I may quote a classic movie, "The only winning move is not to play."
__________________
Bob
Aerospace Engineer '88
RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...
Dues+ Paid 2019,...Thanks DR+
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05-19-2018, 11:17 AM
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Join Date: Oct 2014
Location: Cedar Rapids, IA
Posts: 232
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Quote:
Originally Posted by DanH
(1) You're on the run up pad. How will you determine if the aux feed is actually working?
(2) 8500 ft, smoke in the cockpit. I'm not going to tell you the source. just like you won't know in the air. What will you do?
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1) When I first power up the plane, I'll turn on the ESS Aux feed first and verify power to the ESS Bus and no power to the Main Bus. No need to test that again at the runup pad.
2)See smoke - cut both masters. The ESS bus is now fed by the Aux battery only.
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05-19-2018, 11:53 AM
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Join Date: Jul 2014
Location: West Covina, Ca
Posts: 52
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After a lot of education via this thread, I am thinking of settling on the following power design. Extremely similar to John Brights and others:
On run up, each battery/switch/diode can be tested by alternating power switches.
In flight, my plan would be to have both engine bus switches connected. If either alt/battery goes bad, no pilot intervention would be required. If one side became very problematic, it could be removed.
In an emergency (smoke), both contactors can be opened, hopefully clearing the problem. My last option would be to kill the engine bus.
A lot of research prompted by Carl and Charlie leads me to believe that the diodes and switches can be quite reliable. And a 30amp rated switch should behave well with a max 20amp load.
Looking at: http://ixapps.ixys.com/DataSheet/DSS2x121-0045B.pdf
and: https://www.gamainc.com/product/28a-mtd/
Cole Hersee contactors for Primary and Secondary
Lastly trying to decide on adding a bus tie or not. And I have learned quite a bit from the discussion and appreciate the feedback. Thanks to all.
__________________
Cliff Langlois
Meridian, Idaho
Cliffsrv10.blogspot.com
Project Sold 9/2018
RV-10
Empennage finished!
QB Fuselage and wings in hand
Taking a bite of the elephant every day.
Last edited by Pukauma : 05-20-2018 at 07:32 AM.
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05-19-2018, 12:15 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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I believe Cliff has about the simplest design with two alternators where you can use both power sources to keep the engine running and still isolate the alternators and batteries if there is a problem.
Nothing wrong with human intervention, especially when that intervention is never likely to be required for hundreds or thousands of hours, if ever.
Adding more components for unlikely events doesn't make sense as it may increase the likelihood of failure. Most people who have been in the systems design field for a long time will tell you that.
Last edited by rv6ejguy : 05-19-2018 at 12:21 PM.
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05-19-2018, 12:36 PM
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Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,189
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yep
Well stated.
__________________
Bob
Aerospace Engineer '88
RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...
Dues+ Paid 2019,...Thanks DR+
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05-19-2018, 02:28 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by unitink72
1) When I first power up the plane, I'll turn on the ESS Aux feed first and verify power to the ESS Bus and no power to the Main Bus. No need to test that again at the runup pad.
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That would work. Non-standard, so it would require a bit of pilot training. A pre-start checklist perhaps? After start, it can't be verified without shutting down the main bus, so it's impractical to see if the engine actually runs on the aux source.
Quote:
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See smoke - cut both masters. The ESS bus is now fed by the Aux battery only.
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Engine remains running...unless the aux feed was the smoke source (see your post 110).
Best case (as you say) you're running on one power source. That means half the range before flameout.
Contrast with Cliff's approach. To fire it up, the pilot merely flips on both masters and both engine power supplies. The engine may be run on either power source at any time, for test or otherwise. Opening one or both masters for any reason has no effect on engine operation; power remains dual. Two batteries, so two batteries worth of run time.
Quote:
Originally Posted by rocketman1988
I fly for a living and you guys are scaring me...
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Catchy rant Bob, but that trusty Boeing has separate systems to support the left and right engines, yes? Is there some single electrical failure which would shut down both engines?
The issue is required intervention following silence at a few hundred feet, without CRM, simulator-trained responses, or time. Some intervention may be unavoidable, but less is better, and none is best.
And risk? Yeah, we know we're taking a risk. Design is about reasoned compromise; no design is perfect. The goal is to shave the odds via better choices. Buy a Bus Master if you don't want to think about it.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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05-19-2018, 04:05 PM
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Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,189
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more
Catchy rant Bob, but that trusty Boeing has separate systems to support the left and right engines, yes? Is there some single electrical failure which would shut down both engines?
Can't say for sure Dan, but there IS a checklist for dual engine flameout and loss of all electrical busses, so it must be possible.
The issue is required intervention following silence at a few hundred feet, without CRM, simulator-trained responses, or time. Some intervention may be unavoidable, but less is better, and none is best.
Agree with you there. Unfortunately, to make a system that requires no intervention (or at least minimal intervention) you end up relying on additional mechanical/electrical/solid state devices to provide the required action. This, in turn, can introduce additional failure modes leading you right back to where you started. A mechanical/electrical/solid state device that is 100% reliable would be made from Unobtainium.
And risk? Yeah, we know we're taking a risk. Design is about reasoned compromise; no design is perfect.
Yes Dan, I am very familiar with the design process...especially Spacecraft Design. There is also far more than one way to skin a cat, as they say.
The goal is to shave the odds via better choices.
I agree...but who gets to decide what is better, Dan?
Buy a Bus Master if you don't want to think about it.
Nice childish shot at someone else's design decisions, Dan...and I believe it's called a Bus Manager not a Bus Master...
__________________
__________________
Bob
Aerospace Engineer '88
RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...
Dues+ Paid 2019,...Thanks DR+
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05-19-2018, 05:29 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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People can pine for fully automatic fail overs and properly implemented, they have their place- auto feather systems for instance have probably saved a fair number of lives.
However, then we come down to how to detect and what to do. Have we thought about every possible scenario and a solution or strategy to each? Do we end up with something so complicated that many people won't understand it if something doesn't work as intended?
Remember the CVRs on one Airbus crash- "what is IT doing now?
Automation can be great if it always works, unfortunately it doesn't.
Seems like having the dual power source setup that Cliff depicts is probably as good as the basic power architecture gets with simplicity. Should we leave the ECU switchover in the hands of the pilot or automate it?
How much time will it take to develop and TEST such hardware and software before we trust to use it? What's the liability if the system doesn't save the day if something takes a dump? I'm not sure we have the resources to develop this.
Single engined helicopter folks know the risk of losing the engine at 100-300 feet at low speed airspeed but they still fly them.
Some people want a BRS, other people think they are dead weight.
Always some risk and of course we should take reasonable steps to mitigate most of the ones that may injure us.
In the event of engine stoppage at low altitude, my training (and I do train for this as you all should) is to lower the nose, flip on my backup power switch and my 2nd fuel pump in that order. If I have time, I'll switch tanks. After that, there are not many options left. If Cliff uses both pumps for takeoff and already has 2 power sources feeding the engine bus, he can shave off a couple of these actions.
Last edited by rv6ejguy : 05-19-2018 at 05:34 PM.
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05-19-2018, 06:58 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
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Agree with you there. Unfortunately, to make a system that requires no intervention (or at least minimal intervention) you end up relying on additional mechanical/electrical/solid state devices to provide the required action....
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Not necessarily. Consider Cliff's architecture, or John's. I merely posit that less is better. Ross says getting to none (an automated injector swap) is too difficult, so it looks like one switch flip will stay.
Quote:
Buy a Bus Master if you don't want to think about it.
Nice childish shot at someone else's design decisions, Dan...
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Hey, it's Robert's solution. See post 40. You already an owner?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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05-19-2018, 07:14 PM
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Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,189
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Bus Manager
I do not own a Bus Manager.
I do own A Dual EFII System from Robert.
I am following these discussions as I am currently contemplating the electrical system for my -10.
I am planning on a dual battery, Primary/Standby alternators, EFIS, and EFII system...
__________________
Bob
Aerospace Engineer '88
RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...
Dues+ Paid 2019,...Thanks DR+
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